This invention relates to a refrigeration system which utilizes a swirling nozzle expansion chamber and, in particular, such a system that uses parallel driving and cooling circuits.
In conventional refrigeration systems a working fluid such as a fluorocarbon is cooled through an evaporator where the latent heat of vaporization is obtained from the sensible heat of the fluid, thereby reducing the temperature. In order for such evaporation to occur, the working fluid must be in the liquid state at a pressure below the vapor pressure of the fluid. In many conventional refrigeration cycles, the liquid state is obtained by compressing the fluid to a high pressure and temperature, rejecting the heat to the environment by conduction or convection, and then passing the fluid through a throttling valve to reduce the pressure in a isenthalpic expansion. The liquid then evaporates, absorbs heat, and is returned to the compressor to complete the cycle. This type of refrigeration system has the disadvantages that the compression requires power in the form of expensive mechanical energy, and that the throttling valve returns frictional work to the fluid in the form of heat.
Another type of conventional refrigeration system returns the evaporated working fluid to a liquid by absorbing it into a second liquid, for example, ammonia absorbed into water. The solution is then pumped to a high pressure, and the absorbed working fluid is boiled off by heating. The working fluid then passes through a throttling valve to an evaporator, as in the case of the compression-driven system above. This type of refrigeration system is primarily driven by heat, since the pump requires much less energy than the compressor. This type of system has the disadvantage that the solutions tend to be corrosive, and that the equilibrium is delicate and difficult to control.
An alternate way of expanding and compressing the fluid is through the use of a nozzle and a diffuser. The expansion and compression is approximately isentropic, so that the working fluid is cooled as it expands. This cooling can be used for refrigeration; however, it is difficult to transfer heat to the fluid, which is moving at supersonic velocities. The nozzle/diffuser arrangement can be used as a driver for the compression of a second stream of fluid which is entrained into the driver fluid between the nozzle and the diffuser. Such an arrangement is commonly called an ejector. The flow from the diffuser is a high temperature and pressure. The heat is transferred to the environment, and the fluid, consisting of both the working fluid and the driver fluid is condensed to a liquid. The high pressure liquid stream is divided again into the driver and working fluid streams, with the working fluid passing through a throttling valve to an evaporator, as in conventional systems, before returning to the ejector. Heat is applied to the driver fluid to boil it to a high pressure gas, which is expanded through the nozzle to complete the cycle.
The nozzle/diffuser system can be improved through the use of a configuration in which the major component of the fluid motion is tangential to the axis, thereby producing a swirling motion. The advantages are that the fluid remains in the nozzle longer so that heat transfer to the fluid is facilitated, that the diffuser is more stable, since it is constrained by the conservation of angular momentum, and that the size of a typical nozzle is increased so that fabrication is easier.